The mechanisms of sperm incorporation and the movements of the male pronucleus and the female pronucleus will be studied using time lapse video microscopy of living gametes and zygotes at fertilization. Immersion objectives will be employed to charaterize the actual penetration of the sperm into the egg cytoplasm, whereas polarization, differential interference contrast and phase contrast will be used to visualize the male and female pronuclei within the cytoplasm of the living egg. Microfilament and microtubule inhibitors will be tested to determine the sensitivity of each stage to motility inhibitors. Additionally inhibitors which prevent microfilament and microtubule polymerization or sliding will be employed to evaluate the precise mechanism responsible for each movement. The structures which perform the observed movements will be isolated and characterized by electron and light microscopy, and by protein analytical methods. The egg surface will be examined in relation to presence and state of actin during sperm incorporation. The sperm aster and the pronuclear apparatus will be isolated and characterized to determine the role of microtubules during the nuclear movements.